The invention relates to a control valve mechanism for controlling the flow of hydraulic fluid to and from a hydraulic fluid actuator in a pressurized hydraulic fluid control system. More particularly, it is concerned with valves of the type which are responsive to a pilot pressure for controlling flow of hydraulic fluid to an actuator in a safety system for oil or gas wells.
Pilot valve mechanisms are typically used for responding to pressure variations in a flow system and inducing the actuation of a mechanical device such as a valve actuator, fluid motor or the like. In well safety systems, the mechanisms are usually designed for automatic response to shut down operation of a flow system such as the production line of an oil or gas well whenever pressures in the flowline are outside a predetermined acceptable range. The pilot valves usually include a shuttle valve mechanism which either communicates or interrupts fluid communication of the actuating fluid to the fluid actuator depending on the position of the shuttle valve element with respect to the inlet and outlet of the pilot valve and as induced by the pilot pressure. The mechanisms may also include a bleed port for bleeding the actuating fluid from the fluid actuator to accomplish its deactivation. In many fluid control safety systems where there are long fluid supply lines, quick bleed exhaust valves or "dump" valves have been provided to effect a relatively fast exhaust of fluid from the fluid actuator. U.S. Pat. No. 4,209,040, shows a "dump" valve incorporated in a safety control system for a well having a downwhole safety valve and U.S. Pat. No. 4,041,970 shows a quick bleed exhaust valve for connection between a fluid actuator and a pressurized fluid supply for the quick bleeding of actuating fluid from the actuator. Both of these patents describe a valve for controlling the supply of actuating fluid to a single-acting actuator and the bleeding of actuating fluid when the supply is interrupted. In their "dump" function, these valves must rely on an actuator spring for forcing the ejection of actuating fluid from the control system and if remotely located from the actuator, a relatively long period of time is required. Accordingly, an object of this invention is to provide a unique double acting pilot valve which can be used for effecting the rapid distribution of an actuating fluid to and from a double acting actuator.